Photosynthesis Part III

Purple bacteria

P870 Reaction Center ( pheophytin – quinone system )

Events :

1. Capture of a photon by antenna Chl Chl + hv ----- Chl * ( exciton )

2. Exciton transfer to the Reaction Center (Chl)₂

3. Excitation ( transfer of electron from exciton ) (Chl)_{2 --------} (Chl)₂^*

4. Charge separation (Chl)₂^* + Pheo ------- (Chl) ₂^·+ + Pheo ^{· ˉ} ( t = 3 ps )

5. Electron transfer to bound Q_A ( Manaquinone ) Pheo ^{· ˉ} + Q_A ----- Pheo + Q_A^{· ˉ} (t = 200 ps )
6. Electron transfer to loosely bound Q_B ( ubioquinone ) Q_A^{· ˉ} + Q_B ------- Q_A + Q_B^{· ˉ} ( t = 6 μs )
7. Reduction of Q_B Q_B^{· ˉ} + 2 H⁺ -------- Q_BH₂

8. Diffusion of Q_BH₂ through the membrane to the Cytbc₁ complex

9. Q cycle occurs QH₂ + 2Cytc₁ (oxidized ) + 2H⁺_N = Q + 2Cytc₁ ( reduced ) +4H⁺_P

10. Electron transfer from Cytbc1 complex to (Chl) ₂^·+ via Cyt c₂ (t = 270 ns )